1. Field of the Present Invention
The present invention relates to the field of disk drive storage systems.
2. Background Art
The performance of a disk drive storage system is dependant on the interaction of a number of dynamic and static components and on the precision with which mechanical tolerances between these components can be maintained and controlled. Correspondingly, the effects of differential thermal expansion must be carefully considered and controlled in the design and operation of a disk drive storage system to prevent failures and losses in performance, particularly due to tracking misregistration.
In the prior art, a dedicated servo system is one method employed to provide positioning information to the disk drive system. A servo head having a fixed relationship to one or more data heads is positioned over a servo track, e.g. servo track n, on the dedicated servo surface, defining a data track, e.g. track n'. For typical track dimensions of prior art disk drive storage systems, which are on the order of approximately 1000 tracks per inch (tpi), the dedicated servo approach provides adequate position information. Thermal expansion effects are minimized because the track pitch is within tolerable limits of differential position. That is, if the differential position of the data disk and servo disk is .+-.x, but the track width approximates 5-10x, the data head will still be positioned over servo track n' when the servo head is positioned over track n. However, if the differential position of the data disk with respect to the servo disk, caused by thermal expansion differences of the disks, shafts and other components, exceeds the acceptable limit, the data head could be positioned over track n'+1 when the servo head is positioned over servo track n, leading to read/write errors.
Thus, track density for dedicated servo drives is limited by the differential position of the data disk to the servo disk. This position differential between the data and servo disks is caused by differential thermal expansion between shafts, motors, windings and other associated components due to unequal heat distribution in the head/disk assembly (HDA).
One prior art attempt to achieve higher track density is to use a "wedge" or "sector" servo scheme in which bursts of servo information are interleaved with the data tracks themselves. This attenuates the relative effects of thermal expansion because absolute track position information is provided for each track, as opposed to the relative position information of a dedicated servo system. However, sector servo schemes lack the performance and speed of dedicated servo schemes. After a seek, each head in a cylinder of a sector servo drive must be polled and must wait for a servo sector to pass below to determine position information, adding to seek time and lowering performance.
Thus, it is an object of the present invention to provide a dedicated servo disk drive which permits high track density while attenuating the effects of thermal expansion variations.
It is another object of the present invention to provide a dedicated servo disk drive in which thermally sensitive components are isolated from thermal variation from external sources.
It is yet another object of the present invention to provide a dedicated servo disk drive in which certain internal heat generating components are isolated from thermally sensitive components.
It is still another object of the present invention to provide a dedicated servo disk drive in which thermally sensitive components are disposed in a thermally symmetrical manner to reduce or stabilize differential thermal expansion effects.
Other objects and attendant advantages of the method and apparatus of the present invention will be apparent from the drawings and description of the present invention.